An improved liner hanger running tool is provided for hanging a liner from a casing within a wellbore. The liner hanger running tool includes improvements to a running tool release mechanism, a retrievable packoff bushing, and a packer setting assembly. The packer setting assembly may be used in other downhole sealing applications.
When drilling a well, a borehole is typically drilled from the earth""s surface to a selected depth and a string of casing is suspended and then cemented in place within the borehole. A drill bit is then passed through the initial cased borehole and is used to drill a smaller diameter borehole to an even greater depth. A smaller diameter casing is then suspended and cemented in place within the new borehole. This is conventionally repeated until a plurality of concentric casings are suspended and cemented within the well to a depth which causes the well to extend through one or more hydrocarbon producing formations.
Rather than suspending a concentric casing from the bottom of the borehole to the surface, a liner is often suspended adjacent to the lower end of the previously suspended casing, or from a previously suspended and cemented liner, so as to extend the liner from the previously set casing or liner to the bottom of the new borehole. A liner is defined as casing that is not run to the surface. A liner hanger is used to suspend the liner within the lower end of the previously set casing or liner. Typically, the liner hanger has the ability to receive a tie back tool for connecting the liner with a string of casing that extends from the liner hanger to the surface.
A running and setting tool disposed on the lower end of a work string may be releasably connected to the liner hanger, which is attached to the top of the liner. The work string lowers the liner hanger and liner into the open borehole so that the liner extends below the lower end of the previously set casing or liner. The borehole is filled with fluid, such as a selected drilling mud, which flows around the liner and liner hanger as the liner is run into the borehole. The assembly is run into the well until the liner hanger is adjacent the lower end of the previously set casing or liner, with the lower end of the liner typically slightly above the bottom of the open borehole.
When the liner reaches the desired location relative to the bottom of the open borehole and the previously set casing or liner, a setting mechanism is conventionally actuated to move slips on the liner hanger from a retracted position to an expanded position and into engagement with the previously set casing or liner. Thereafter, when set down weight is applied to the hanger slips, the slips are set to support the liner.
The typical liner hanger may be actuated either hydraulically or mechanically. The liner hanger may have a hydraulically operated setting mechanism for setting the hanger slips or a mechanically operated setting mechanism for setting the slips. A hydraulically operated setting mechanism typically employs a hydraulic cylinder which is actuated by fluid pressure in the bore of the liner, which communicates with the bore of the work string. When mechanically setting the liner hanger, it is usually necessary to achieve relative downhole rotation of parts between the setting tool and liner hanger to release the hanger slips. The hanger slips are typically one-way acting in that the hanger and liner can be raised or lifted upwardly, but a downward motion of the liner sets the slips to support the hanger and liner within the well.
To release the running tool from the set liner hanger, the setting tool may be lowered with respect to the liner hanger and rotated to release a running nut on the setting tool from the liner hanger. Cement is then pumped down the bore of the work string and liner and up the annulus formed by the liner and open borehole. Before the cement sets, the setting tool and work string are removed from the borehole. In the event of a bad cement job, a liner packer and a liner packer setting tool may need to be attached to the work string and lowered back into the borehole.
The packer is set utilizing a packer setting tool. Packers for liners are often called xe2x80x9cliner isolationxe2x80x9d packers. A typical liner isolation packer system includes a packer element mounted on a mandrel and a seal nipple disposed below the packer. The seal nipple stings into the tie back receptacle on top of or below the previously set and cemented liner hanger. A liner isolation packer may be used, as explained above, to seal the liner in the event of a bad cement job. The liner isolation packer is typically set down on top of the hanger after the hanger is secured to the outer tubular, and the packer is set by the setting tool to seal the annulus between the liner and the previously set casing or liner.
Generally, the deeper a well is drilled, the higher the temperature and pressure which is encountered. Thus, it is desirable to have liner packers which will ensure quality cementing of the liner so as to provide a high safety factor in preventing gas from the formation from migrating up the annulus between the liner and outer casing.
During the cementing operation, fluid such as drilling mud in the annulus between the liner and outer casing is displaced by cement as the cement is pumped down the flow bore of the work string. First, the drilling mud and then the cement flows around the lower end of the liner and up the annulus. If there is a significant restriction to flow in the annulus, the flow of the cement slows and a good cementing job is not achieved. Any slowing of the cementing in the annulus allows time for the gas in the formation to migrate up the annulus and through the cement to prevent a good cementing job.
Running Tool Release Mechanism
As a practical matter, the liner hanging running tool must include a release mechanism so that, once the liner is reliably set to the lower end of the casing, the running tool can be released from the liner hanger and retrieved to the surface. Conventional liner hanger running tool releasing mechanisms include hydraulically actuated mechanisms, and release mechanisms that are manipulated by left-hand rotation of the running string. The left-hand rotation of the running string is, however, generally considered undesirable since it may result in an unintended disconnection of one of the joints of the running string, thereby causing separation of the running string and a fishing operation to retrieve the running tool, which may have been damaged by the unintended disconnection. For various reasons, hydraulically operated running tool release mechanisms may fail to operate, or may prematurely release the running tool from the liner hanger.
Accordingly, improvements in release mechanisms are desired which will reliably release the running tool from the set liner only when intended, particularly when retrieving is easily accomplished and premature disengagement of the running tool from the liner is highly unlikely.
Packoff Bushing
A liner hanger packoff bushing conventionally seals between the liner hanger and the running tool, and thus between the liner and the running string or work string, which conventionally may be drill pipe. A packoff bushing is particularly required during cementing operations so that fluid pumped through the drill pipe continues to the bottom of the well and then back up into the annulus between the well bore and the liner to cement the liner in place. During cementing operations, the seal body of the packoff bushing is fitted in the annulus between the liner hanger and the running tool, and includes OD seals for sealingly engaging the liner hanger and ID seals for sealingly engaging the running tool. Packoff bushings are preferably retrievable with the running tool to prevent having to drill out the bushings after the cementing operation is complete. Also, a packoff bushing is preferably lockable to the liner hanger by locking within a profile to prevent the bushing from moving axially with respect to the liner hanger. If the packoff bushing is not lockable to the profile of the liner hanger, the bushing may get xe2x80x9cpumped outxe2x80x9d through the top of the receptacle, thereby losing a cementing job.
A conventional retrievable and lockable packoff bushing includes metal dogs or lugs which are locked into engagement with the liner hanger to prevent the packoff bushing from moving axially during the cementing operation. The packoff bushing is retrievable with the running tool, and thus eliminates the need to drill out the bushing after cementing operations are complete. Depending on the manufacturer, retrievable packoff bushings are also referred to as retrievable seal mandrels or retrievable cementing bushings. Regardless of the terminology, the retrievable and lockable packoff bushing seals the annulus between the running string and the top of the liner, and may be locked in a profile of the liner hanger by the slick joint to prevent the bushing from being pumped out of the liner hanger.
Cooperating surfaces on the liner running adapter, the slick joint on the running tool, and the seal body of the packoff bushing axially interconnect the bushing to the liner hanger while running the liner hanger into the well. These cooperating surfaces may be unlocked to release the running tool from the liner hanger and allow axial manipulation of the running tool and slick joint relative to the packoff bushing. The slick joint thus seals with the packoff bushing during axial movement of the running tool. Once the cooperating surfaces are unlocked from each other, shoulders on the packoff bushing and the running tool engage after a predetermined amount of axial movement between the running tool and the seal body, so that the packoff bushing may be retrieved to the surface with the running tool after the cementing operations is complete. A conventional packoff bushing is disclosed in U.S. Pat. No. 4,281,711.
A significant limitation on prior art packoff bushings concerns their desired retrievability with the running tool, when coupled with the desire to pick up the running tool relative to the packoff bushing before the cementing operation. An operator will typically want to pick up the running tool after release from the liner hanger to ensure that these tools are disconnected. The length of the running tool slick joint determines the maximum length that the running tool should be picked up after release from the liner hanger. When the packoff bushing is pulled out of the liner hanger, the dogs or lugs conventionally carried by the packoff bushing are allowed to move radially inward, thereby preventing the retrievable packoff bushing from being stabbed back into and locked into the liner hanger. Conventional liner hanger running tools do not allow the packoff bushing to be xe2x80x9cre-stabbedxe2x80x9d into the liner hanger and thereby re-establish pressure integrity between the liner hanger and the running tool. In many applications, it is difficult for the operator to determine the exact amount the running tool has been picked up, particularly when operating in deep or highly deviated wells. If the operator picks up the running tool an axial distance not permitted by the length of a slick joint, the packoff bushing will be pulled up with the running tool and will disengage from the liner hanger, which may cause a cementing failure costing the operator millions of dollars in lost time and money. The consequences of unintentionally unseating the packoff bushing from the liner hanger and not being able to re-stab and lock into the liner hanger may thus be severe.
The slick joint used with the liner hanger running tool has a polished OD surface which seals against the ID seals on the seal body of the packoff bushing. The slick joint OD surface can become scratched or damaged during handling, thereby causing a cementing leak during the cementing operation. Since the running tool is designed to move axially substantial distances relative to the packoff bushing, the inner seals on the seal body may wear out during the cementing process due to the reciprocation of the running tool slick joint. This problem is exacerbated when the quality of the polished surface on the slick joint has deteriorated. Axially long slick joints are expensive to manufacture and maintain.
Another problem with prior art packoff bushing concerns the limited load capacity of the lugs that lock the packoff bushing to the liner hanger. Conventional packoff bushings utilize multiple lugs protruding from the packoff seal body, which increases the complexity and the cost of the packoff bushing. The limited size of these lugs nevertheless restricts or limits the cementing pressure capacity of the packoff bushing.
Packer Setting Assembly
A conventional liner hanger running tool includes a packer setting assembly, which allows the activation and packoff of the liner top packer. Conventional packer setting assemblies incorporate multiple spring-loaded dogs or lugs which may be compressed to a reduced diameter position by insertion into the packer setting sleeve when running the liner hanger in the well and when cementing the liner within the casing. When the packer setting assembly is raised out of the packer setting sleeve, the dogs or lugs expand to a diameter greater than the ID at the upper end of the setting sleeve, which is also the tie back receptacle of the liner hanger. When the dogs engage the top of the setting sleeve, a setting force may be transferred from the running string through the dogs and to the packer setting sleeve as running string weight is slacked off to set the packer element.
Some prior art packer setting assemblies include an axial bearing to facilitate rotation of the work string while setting the packer element. Other packer setting assemblies include both a bearing and a shear indicator to provide a visual confirmation that the proper setting load was applied to the packer, and/or an unlocking feature that allows the packer setting assembly to be pulled out of the packer setting sleeve one time without exposing the setting dogs. This latter tool allows re-stabbing the packer setting assembly into the packer setting sleeve one time, thereby arming the setting dogs so they are ready to expand the second time the dogs are pulled out of the setting sleeve.
A primary problem concerning prior art packer setting assemblies is poor reliability. In some well environments, the packer setting dogs of conventional packer setting assemblies collapse and re-enter the setting sleeve without setting he packer element. Manufacturers have provided more dogs or lugs to alleviate this problem, and/or have provided heavier springs to bias the dogs radially outward. These changes have had little if any affect on achieving higher reliability.
The disadvantages of the prior art are overcome by the present invention, and an improved liner hanger running tool is hereinafter disclosed which includes improvements to a running tool release mechanism, a retrievable packoff bushing, and a packer setting assembly. In addition, the improved packer setting assembly may be used in operations not involving a liner hanger running tool.
A preferred embodiment of a liner hanger running tool of the present invention includes improvements to one or more of the running tool release mechanism, the retrievable packoff bushing and the packer setting assembly. The running tool may be used for positioning a liner within a casing in a wellbore and subsequently cementing the liner in place, then retrieving the running tool to the surface with the packoff bushing and the packer setting assembly. The packer setting assembly may be used in other downhole packer setting applications.
Running Tool Release Mechanism
The liner hanger running tool release mechanism preferably includes a hydraulically actuated mechanism for releasing the running tool from the set liner hanger in response to fluid pressure within the running tool, and also a mechanical right-hand release mechanism which, if necessary, allows the running tool to be mechanically released from the liner hanger by right-hand rotation of the work string. The combination of the hydraulic release mechanism and the right-hand release mechanism significantly improves reliability of the running tool.
It is an object of the present invention to provide an improved running tool release mechanism for releasing a running tool from a set liner hanger. The running tool may be hydraulically released, but also may be released by right-hand rotation of the running string. A first piston is used for hydraulic release. A second piston is used to disengage a clutch, thereby allowing a nut to move downward along the right-hand threads on the running tool mandrel due to right-hand rotation of the running string. Once the nut has moved axially downward on the mandrel, the work string may be picked up to disengage the running tool from the liner hanger.
Yet another feature of the invention is that, after the clutch has been disengaged to allow right-hand release of the running tool, fluid pressure may be used to reengage the clutch to allow rotation of the liner during a cementing operation.
Yet another feature of the invention is that fluid within the running tool which transmits fluid pressure to the piston for hydraulic release of the running tool may be isolated by a sleeve, such that the sleeve shifts downward to expose a port and allow hydraulic fluid to release the running tool.
A significant feature of the running tool release mechanism is that the release mechanism may be actuated both hydraulically and by right-hand rotation of the running string or work string.
A related feature of the running tool release mechanism is that reliability of the release operation is significantly improved with little if any cost increases.
Packoff Bushing
During the cementing operation, the packoff bushing serves its function of providing a seal between the liner hanger and the running string. The packoff bushing may be axially fixed to the liner hanger during the cementing operation by a C-shaped lock ring, which is held locked in a groove in the liner hanger by a fluid pressure responsive piston. The packoff bushing is designed such that it may be reinserted into the liner hanger when the packoff bushing is raised with the running string relative to the set liner hanger. Accordingly, the cost of the slick joint may be avoided. The liner hanger packoff bushing may thus be removed from the liner hanger when the operator picks up the running tool to check for release of the running tool from the liner hanger and verify that the liner is properly set in the casing. When the running tool is slacked back off into the liner hanger before pumping cement, the packoff bushing can be re-stabbed and resealed to the liner hanger. When pressure is subsequently applied to the running string during a cementing operation, the packoff bushing will be locked to the liner hanger by the fluid pressure to prevent movement out of the liner hanger. Fluid pressure thus keeps the packoff bushing locked to the liner hanger, while the absence of pressure in the running string allows the packoff bushing to be picked up out of the liner hanger and subsequently reinserted into the liner hanger. The liner hanger running tool thus includes a packoff bushing which may be repeatedly xe2x80x9cre-stabbedxe2x80x9d back into the liner hanger, as desired by the operator, to re-establish pressure integrity between the running tool and the liner hanger.
By providing a re-stabbable packoff bushing, the operator has much more flexibility when picking up to check for release of the running tool. By providing a packoff bushing which may be repeatedly reinserted into the liner hanger so that a seal may be repeatedly established between the running string and the liner hanger, the operator avoids much of the risk of a bad cementing job, and the significant loss of time and money to correct a bad cementing job. The re-stabbable packoff bushing may be used on a running tool with or without a liner hanger packer for sealing between the casing and the liner hanger.
The packoff bushing is preferably designed with a C-shaped lock ring to increase the cementing pressure capability of the packoff bushing. Compared to prior art packoff bushings, the one-piece lock ring avoids the use of multiple lugs and springs which add length and complexity to the packoff bushing without significantly increasing the cementing pressure capability of the packoff bushing when locked to the liner hanger.
It is an object of the present invention to provide a liner hanger running tool with the packoff bushing which may be repeatedly restabbed into the top of the liner.
A feature of this invention is that the packoff bushing incorporates a C-shaped one-piece lock ring, which effectively locks the packoff bushing to the liner hanger in response to fluid pressure, which acts on a piston to retain the lock ring in the locked position. The absence of fluid pressure allows the lock ring to be collapsed, thereby permitting the restabbing of the packoff bushing into the top of the liner hanger. The C-shaped lock ring may include radially external or internal slots for facilitating expansion and contraction of the lock ring.
The packoff bushing includes a radially outer shoulder for engaging a radially inner shoulder on the liner hanger when the lock ring is aligned with the groove in the liner hanger, so that set down weight may be applied to the liner hanger. The packoff bushing also includes a radially inner shoulder, so that the packoff bushing is retrieved with the tool to the surface. In addition to the packoff bushing, the running tool may include a packer setting assembly for activating the packer element to seal between the casing and the liner hanger.
It is a feature of the invention that the running tool may include a retrievable packoff bushing which may be reinserted or xe2x80x9crestabbedxe2x80x9d into the liner hanger numerous times. A related feature of the invention is that the cost of a slick joint may be avoided.
It is a further feature of the present invention to provide an improved liner hanger running tool packoff bushing wherein fluid pressure keeps the packoff bushing locked to the liner hanger, while the absence of fluid pressure may allow the packoff bushing to be picked up out of the liner and subsequently reinserted into the liner. A related feature of the running tool with the improved packoff bushing is the reduced risk of a bad cementing job.
Packer Setting Assembly
The packer setting assembly may be used with the liner hanger running tool to set the liner top packer after the liner hanger has been set, and after the running tool has been released from the liner hanger. The packer setting assembly may be positioned on the running tool at a desired location, which may be axially between the liner hanger releasing assembly and the slip setting assembly at the lower end of the running string or work string. When the running tool is assembled at the surface, the packer setting assembly is thus contained within the tie back receptacle or setting sleeve of the liner hanger assembly.
The packer setting load is preferably transferred to the packer setting sleeve through a one piece C-shaped setting ring. The C ring design enables more weight to be set down on the setting sleeve than with the plurality of dogs used in the prior art. A lock out feature keeps the setting ring in weight-transfer engagement with the setting sleeve so that the setting ring will not prematurely snap radially inward toward the packer setting housing before the packer is set. Seals on both the ID and the OD of the packer setting assembly also aid in setting the packer. Once the initial load has been set down on the liner hanger, the ID seal which seals to the running tool mandrel, and the OD seal which seals to the setting sleeve, act as a piston responsive to pressure applied to the annulus to assist in setting the packer element. This fluid pressure assist along with the set down weight achieves the proper setting force to the liner top packer element. By using annulus pressure to aid in setting the packer element, a significant additive hydraulic force complements the set down weight to reliably set the liner hanger packer element.
A preferred packer setting assembly includes an unlocking feature that allows the assembly to be pulled out of the packer setting sleeve one time without releasing a setting ring. Upon re-stabbing the assembly into the setting sleeve, the packer setting ring becomes activated and is ready to expand the second time the packer setting assembly is pulled out of the setting sleeve. An adjustable shear indicator may be included to provide immediate visual confirmation, when the running tool is retrieved to the surface, that adequate setting force was applied to the liner top packer. A bearing assembly in the packer setting tool allows rotation and slack off of the running string without damaging the packer setting sleeve or setting ring. Rotation also breaks the static friction between the running string and the casing, thereby reducing buckling and insuring maximum transfer of setting force to the liner packer element.
It is an object of the present invention to provide a packer setting assembly which uses an expandable and collapsible one-piece C-ring to set weight down to a packer element. The packer setting assembly also includes O.D. seals and I.D. seals, so that fluid pressure may be used to increase the setting force applied to the packer element.
It is a feature of the packer setting assembly according to the present invention that the C-ring may be locked in a collapsed position by a locking mechanism to prevent the C-ring from moving to its expanded position. This allows the packer setting assembly to be pulled out of the tie back receptacle one time without releasing the C-ring, and allows the lockout mechanism to engage the top of the tie back receptacle for weight set down. The next time the packer assembly is pulled out of the tie back receptacle, the C-ring is allowed to expand radially outward for engagement with the top of the tie back receptacle.
It is a further feature of the present invention that the packer setting assembly has multiple uses. The packer setting assembly may be used as part of a liner hanger running tool, although the packer setting assembly may also be used for other applications wherein an operator desires to radially set a downhole packer.
It is a feature of the invention that the packer setting assembly transfers the packer setting load to the packer setting sleeve through a C-shaped setting ring.
A related feature is that seals on both the I.D. and O.D. of the packer setting assembly may assist in setting the packer.
Yet another feature of the packer setting assembly is that the setting ring may be easily and reliably locked out to prevent premature actuation.
Yet another feature of the packer setting assembly is that it may include an unlocking feature so that the assembly may be pulled out of the packer setting sleeve one time without releasing the setting ring.
An advantage of the improvements to each of the running tool release mechanism, the retrievable packoff bushing, and the packer setting assembly is that these mechanisms rely upon components which have been found highly reliable in the oilfield services industry. The complexity of the running tool with one or more of these features is not significantly increased and, in many cases, is made simpler. Tool reliability has been increased to perform the desired downhole operations.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.